\begin{tabular}{lcccccccc} \\\toprule
 & \multicolumn{8}{c}{Results for $\rho$} \\ 
 & \multicolumn{4}{c}{Bias} & \multicolumn{4}{c}{Std. Dev.} \\ 
& (1)& (2)& (3)& (4)& (1)& (2)& (3)& (4)\\ 
\cmidrule(r){2-5}\cmidrule(r){6-9}$N$ = 500 & 17.80 & 24.52 & 0.31 & 14.59 & 23.30 & 23.78 & 1.21 & 21.12\\ 
$N$ = 1000 & 13.72 & 28.82 & 0.09 & 8.92 & 20.99 & 23.03 & 0.73 & 17.56\\ 
$N$ = 5000 & 1.78 & 28.27 & 0.02 & 0.52 & 7.41 & 21.94 & 0.29 & 2.62\\ 
&&&&&&&& \\ 
 & \multicolumn{8}{c}{Results for $a$} \\ 
 & \multicolumn{4}{c}{Bias} & \multicolumn{4}{c}{Std. Dev.} \\ 
& (1)& (2)& (3)& (4)& (1)& (2)& (3)& (4)\\ 
\cmidrule(r){2-5}\cmidrule(r){6-9}$N$ = 500 & -0.02 & -0.02 & 0.00 & 0.01 & 0.34 & 0.40 & 0.04 & 0.31\\ 
$N$ = 1000 & 0.00 & -0.01 & 0.00 & 0.00 & 0.30 & 0.38 & 0.03 & 0.25\\ 
$N$ = 5000 & 0.00 & -0.02 & -0.00 & 0.00 & 0.14 & 0.30 & 0.01 & 0.10\\ 
&&&&&&&& \\ 
 & \multicolumn{8}{c}{Results for $\delta$} \\ 
 & \multicolumn{4}{c}{Bias} & \multicolumn{4}{c}{Std. Dev.} \\ 
& (1)& (2)& (3)& (4)& (1)& (2)& (3)& (4)\\ 
\cmidrule(r){2-5}\cmidrule(r){6-9}$N$ = 500 & -0.00 & -0.00 & 0.00 & -0.00 & 0.02 & 0.02 & 0.02 & 0.02\\ 
$N$ = 1000 & -0.00 & -0.00 & 0.00 & -0.00 & 0.01 & 0.01 & 0.01 & 0.01\\ 
$N$ = 5000 & 0.00 & 0.00 & 0.00 & -0.00 & 0.01 & 0.01 & 0.01 & 0.01\\ 
\bottomrule\end{tabular}